Predicting the time–swell relationship of an unsaturated highly expansive clay using the heat equation

Although extensive research and practical experience have established a good understanding of the magnitude of swell in unsaturated expansive clays due to wetting, significantly less is known regarding the time taken for the swelling strains to develop. This paper describes a mathematical model, based on analogies with conventional consolidation theory and the heat equation, to predict the time-dependent volume increase during swelling of an initially unsaturated expansive clay. A series of oedometer tests on a highly expansive clay was performed to determine the coefficients of swell used in the proposed model. The observed oedometer swelling curves showed good agreement with the theoretical relationship. The results were then used to predict swell over time in a layered centrifuge model constructed from the same clay. The predicted heave closely matched the observed result at any time over an 11-year swelling period in prototype time.